The present invention relates to a die set for manufacturing fins of heat exchangers and a manufacturing device using the same. More precisely, the present invention relates to a die set comprising a punch and a die for forming a projected section, which is formed along an edge of a hole bored in a metal plate, into a collar with a prescribed height and a manufacturing device using the same.
Heat exchangers for car radiators, room air conditioners, etc. have heat exchanging fins, which are made of thin, rectangular metal (e.g. aluminum) plate and in which a multiplicity of through-holes with collars are bored.
In the heat exchangers, a plurality of fins are stacked such that their through-hole coincide, then tubes which are made of a highly thermal conductive metal such as copper are inserted through the coincidental through-holes so as to assemble the fins as a single heat exchanger.
A method of manufacturing the above described fins was disclosed in the U.S. Pat. No. 4,055,067. This method will be described with reference to FIGS. 10A-10D.
First, a through-hole 101 is bored into plate 100, and then the edge of the through hole 101 is rounded into a projected section 102 by a burring process (see FIG. 10A) wherein the edge of the through-hole 101 is stamped to form a circular, raised surface, e.g. said projected section 102.
Next, the diameter of the through-hole 101 is enlarged and the projected section 102 is ironed to form the projected section 102 into a collar 104 with a prescribed height (see FIGS. 10B and 10C), wherein the ironing process is the pressing of the projected section against an interior wall of a die and the deforming of the projected section primarily from the interior face by a circumferential corner section of a punch inserted into the die.
In FIGS. 10B and 10C, the ironing step is executed twice and the diameter of punch and die for the first step is different from that of the second step.
The upper end of the collar 104, which is formed by the above described ironing operation, is then bent to form a flange 105 (see FIG. 10D).
The above described method is executed by a punch and a die as shown in FIGS. 11A and 11B.
The metal plate 100 is held between a die 110 and a stripper-plate 112, and the projected section 102 is inserted into a hollow section of the die 110 (see FIG. 11A).
Next, the diameter of the through-hole 101 is enlarged by a punch 114, which moves upward from the level of the metal plate 100, so that the projected section 102 is ironed to form the collar 103 with a prescribed height (see FIG. 11B).
The ironing operation is executed by an ironing section 116, which is formed in the upper end section of the punch 114, and the inner face of the die 110, which corresponds to the ironing section 116 when the punch 114 enters the die 110.
In the ironing operation shown in FIGS. 11A and 11B, involatile oil is usually used as machining oil. When involatile oil is used, some of the oil remains on the ironed fin. To remove the oil, Freon has been used. However, Freon's usage has been limited because of its impact on the environment, and it may be prohibited in the near future to use Freon as a solvent for cleaning the residual oil.
To solve this problem, the inventors tried to use volatile oil instead of involatile oil so as to enable cleaning of the ironed fin without using Freon. However, when using volatile oil, the malleability of the metal plate 100 is less in comparison to the case of using involatile oil. Therefore, the resulting height of the collar is quite lower.
Currently, when using thin and hard metal plates to form fins, it is very difficult to form significantly higher collars because of the lower malleability caused by volatile oil.
Moreover, hydrophile coated metal plates (e.g. hydrophile coated aluminum plate) are used because of increased thermal conductivity. If a hydrophile coated metal plate is ironed by the punch and the die shown in FIGS. 11A and 11B at the ordinary ironing rate, the hydrophilic coating on the inner face, which is the face ironed, is peeled off. A heat exchanger having fins whose hydrophile coating was peeled off cannot perform the designed heat exchange. The inventors thought that if the projected section 102 is formed without ironing or without substantial ironing, the destruction of the hydrophilic coating can be prevented.